1. Field of the Invention
This invention relates to a process of preparing a vinyl chloride polymer, and more particularly to a process of preparing vinyl chloride polymer, that can prepare a vinyl chloride polymer of high quality with a high productivity.
2. Description of the Prior Art
In preparing vinyl chloride polymers, it may sometimes occur that, after a polymerization initiator has been fed into a polymerization vessel through charging passage comprising a charging pipe, etc., the polymerization initiator sticks on the inner wall of the charging passage, particularly at a charging port positioned at the end of the charging passage to remain there. The polymerization initiator remaining like this reacts with a monomer during the polymerization, resulting in formation of polymer scale. Since the polymer scale may grow to clog the charging passage, particularly at the charging port, the grown polymer scale must be removed.
As methods of removing the polymerization initiator having stuck and remained in the charging passage and of preventing formation of the polymer scale, proposed are a method in which the charging passage is washed with an organic solvent, a method in which the charging port is closed to block the invasion of the monomer from the inside of the polymerization vessel, etc.
However, in the former method, in which the charging passage is washed with an organic solvent, a large quantity of organic solvent is required for completely removing the polymerization initiator having stuck and remained therein, so that the solvent remains in a manufactured polymer to cause a lowering of quality, and generation of an ill smell when the polymer is molded or formed. Hence, there is a limit on the amount of the organic solvent to be used, and thus the washing can not be thoroughly performed. As the results, the polymerization initiator remains more or less, bringing about the problem that the polymer scale are still formed if the polymerization is carried out for a long period of time. In the latter method, in which the charging port is closed, there has been the problem that the monomer invades into the charging passage from a gap in the closed charging port resulting in the formation of polymer scale.
There has been also proposed a method in which the polymerization initiator is charged as an aqueous emulsion in order to reduce the amount of an organic solvent to be used. This method can make it avoidable that the organic solvent remains in a manufactured polymer, but yet it is difficult to prevent the polymerization initiator from sticking and remaining in the charging passage, and to prevent the scale formation in the charging passage.